Thermoplastic polyester molding composition having an improved impact performance

Abstract

The invention relates to a thermoplastic molding composition comprising a blend of a thermoplastic polyester and a reinforcing amount of a reinforcing agent. An improvement in the impact performance of the composition is disclosed to result upon the incorporation therewith of a blocked (end-capped) polyisocyanate prepolymer.

What is claimed is: 
     
       1. A thermoplastic molding composition comprising a blend of (i) polyethylene terephthalate,   (ii) a reinforcing amount of a reinforcing agent of said polyethylene terephthalate and   (iii) about 0.5 to about 8.0 parts per hundred weight of said polyethylene terephthalate of an end-capped polyisocyanate prepolymer.   
     
     
       2. The molding composition of claim 1 wherein said reinforcing agent is glass fibers. 
     
     
       3. The molding composition of claim 1 wherein said polyisocyante prepolymer is derived from (a) an organic polyisocyanate corresponding to   Q(NCO).sub.n     wherein n is 2-4 and Q denotes a C 2  -C 18  saturated aliphatic hydrocarbon radical, C 4  -C 15  saturated cycloaliphatic hydrocarbon radical, C 6  -C 15  aromatic hydrocarbon radical or a C 8  -C 15  arylaliphatic hydrocarbon radical with the proviso that at least 2 carbon atoms are present between the NCO-groups in each case and (b) an organic compound containing at least two isocyanate-reactive groups characterized in that its molecular weight is about 60 to about 10,000 and in that the backbone of the resulting prepolymer is substantially immiscible in said polyethylene terephthalate.   
     
     
       4. The molding composition of claim 3 wherein said isocyanate-reactive group is selected from the group consisting of amino, thiol, carboxyl and hydroxyl radicals. 
     
     
       5. The molding composition of claim 3 wherein said (b) is a hydroxyl compound selected from the group consisting of hydroxy polyethers, hydroxy polyolefins, hydroxy polybutadienes, hydroxy polycarbonates and hydroxy polyester amides. 
     
     
       6. The molding composition of claim 3 wherein said organic polyisocyanate is at least one member selected from the group consisting of tetramethylenediisocyanate, hexamethylene-diisocyanate, dodecamethylene-diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane, 2,4-hexahydrotoluene-diisocyanate, 2,6-hexahydrotoluene diisocyanate, hexahydro-1,3-phenylene diisocyanate, hexahydro-1,4-phenylene diisocyanate, perhydro-2,4'-diphenylmethane diisocyanate, perhydro-4,4'-diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, diphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate and naphthylene-1,5-diisocyanate. 
     
     
       7. The molding composition of claim 3 wherein said organic polyisocyanate is at least one member selected from the group consisting of hexamethylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane, diphenylmethane-4,4'-diisocyanate, dicyclohexyl methane-4,4'-diisocyanate, 2,4-toluene diisocyanate and 2,6-toluene diisocyanate. 
     
     
       8. The molding composition of claim 1 wherein said polyisocyanate prepolymer is characterized in that it is blocked by an agent selected from the group consisting of secondary alcohols, tertiary alcohols, C-H acid esters, ketones, triazoles, oximes, lactams, phenols, amides, imides, imidazoles, bisulphites and hydroxy-substituted nitrogen compounds. 
     
     
       9. A thermoplastic molding composition comprising a blend of (i) polyethylene terephthalate resin,   (ii) about 10 to about 50 percent relative to the weight of said blend, of reinforcing glass fibers and   (iii) about 0.5 to about 8.0 parts per one hundred parts by weight of said resin, of a blocked polyisocyanate prepolymer which is the polyaddition reaction product of toluene diisocyanate and hydroxy polyether which product is blocked by ε-caprolactam.   
     
     
       10. A thermoplastic molding composition comprising the extruded blend of (i) polyethylene terephthalate,   (ii) a reinforcing amount of a reinforcing agent of said polyethylene terephthalate and   (iii) about 0.5 to about 8.0 parts per hundred weight of said polyethylene terephthalate of an end-capped polyisocyanate prepolymer.   
     
     
       11. The thermoplastic molding composition of claim 10 wherein said (iii) is present at an amount of about 1.0 to about 5.0 parts per hundred weight.